This invention generally relates to image-forming machines having a development station for an eletrophotographic process. More particularly, this invention relates to image-forming machines having a sensing device for monitoring the developer flow properties in the development station.
Image-forming machines transfer images onto paper or other medium using an electrophotographic process. An image-forming machine typically has a photoconductor, one or more chargers, an exposure machine, a development station, a fuser station, and a cleaning station. The image-forming machine also may have a logic control unit (LCU) or other microprocessor, a graphic user interface, and other components.
The photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. The development station deposits toner onto the photoconductor surface. The toner is charged and thus adheres to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred onto a sheet of paper or other medium. In the fuser station, the sheet is heated causing the toner to fix or adhere to the paper or other medium. The photoconductor is refreshed, cleaned to remove residual toner and charge, and then is ready to make another image. The sheet exits the image-forming equipment.
At the development station, toner is attracted to the photoconductor under the influence of an electric field. The development station stores and mixes a developer, which may be mono-component or bi-component. A mono-component developer comprises toner. A bi-component developer comprises a mixture of toner and a carrier. Toner is the marking material in an image-forming machine and usually comprises a polymer, a pigment, and a charging agent. Carrier is a transport media and comprises magnetic particles typically made of iron or an iron-based material. The mixing of the developer tribo-electrically charges the toner in a mono-component system and the toner and carrier in a bi-component system. The toner is transported to a development region adjacent to the photoconductor. The electric field in the development region transfers the toner from the development station to the photoconductor. Portions of the surface having the electrostatic latent image attract the toner. The toner turns the electrostatic latent image into a visible image. Portions on the surface not having the electrostatic latent image do not attract the toner.
Many image-forming machines have a toner monitor in the development station. The toner monitor generally is a magnetic sensing device that provides a output voltage responsive to the toner concentrationxe2x80x94the ratio of the toner to carrier in the developer mix. The toner monitor also may be an electrical or optical sensing device. The logic control unit (LCU) in the image-forming machine uses the output voltage to determine when to replenish toner in the development station.
Most image-forming machine do not measure a change in the flow properties of the developer in the development station. Setup and operation of a development station typically assumes that material properties will remain essentially constant. Typically, an image-forming machine has little or no way to identify a change in material flow properties other than a visual difference. The material flow properties of the developer may change due to one or a combination of factors such as the material characteristics of the developer, the variability of properties in the developer, and the environmental conditions during the storage and use of the developer. Environmental conditions include temperature, humidity, pressure, impurities, and the like. Many image-forming machines have a warming device in the development station to reduce the effect of humidity and temperature variation on the developer.
In addition, an image-forming machine usually has little or no way to identify when hardware changes have modified the material flow of the developer. These hardware changes may occur from servicing the image-forming machine, performing maintenance on the image-forming machine, and operating the image-forming machine. During service and maintenance, the hardware in the image-forming machine may be adjusted or repositioned. During operation, the flow properties may vary due to the variability in operation of the image-forming machine such as when the development station starts and ends mixing of the developer. Other hardware changes may affect the flow properties of the developer.
Improper material flow in a development station may result in poor mixing and poor delivery of the toner to the photoconductor. With improper material flow, developer may accumulate on the inside of the development station. New toner may flow pass the accumulated developer without mixing properly with the developer. This improperly flowing toner may have a poor tribo-electric change and may have an uneven concentration when transported to the photoconductor. The improper material flow may cause image-quality defects such as fogging and fading. Fogging occurs when too much toner attaches to the image. Fading occurs when too little toner attaches to the image. The fogging and fading may appear on the same image.
The improper material flow may result in improper adjustments to the toner concentration. Some image-forming machines increase the aim toner concentration as the imaging cycles through the development station increase. The toner concentration also may be increased in response to a fading defect. However, the fading maybe the result of an improper tribo-electric change and not due to a low concentration of toner. Other image-quality defects and operational difficulties may result from improper material flow.
This invention provides a development station with a developer flow monitoring system for an image-forming machine. The developer flow monitoring system senses the material flow of a developer in the development station.
In one aspect, an image-forming machine one or more chargers, an exposure machine, and a development station operatively connected to a photoconductor. The chargers electrostatically charge the photoconductor. The exposure machine forms an electrostatic image on the photoconductor. The development station applies toner on the photoconductor. The development station has a material flow sensing device mounted on a developer sump. The material flow sensing device generates a material flow signal in response to a material flow of a developer in the developer sump.
In another aspect, a development station for an image-forming machine has a ribbon blender, a bucket assembly, and a toning roller operatively mounted in a developer sump. The development station also has a material flow sensing device mounted on the developer sump. The material flow sensing device generates a material flow signal in response to a material flow of a developer in the developer sump.
In a method for monitoring material flow in a development station of an image-forming machine, a material flow signal is generated in response to a material flow of a developer in the development station. The material flow signal is compared to a reference flow signal.
Other systems, methods, features, and advantages of the invention will be or will become apparent to one skilled in the art upon examination of the following figures and detailed description. All such additional systems, methods, features, and advantages are intended to be included within this description, within the scope of the invention, and protected by the accompanying claims.